1. Technical Field
The present invention relates to a hand-held resistance welding tool. The welding tool of the present invention is particularly useful for installing a mesh anode cathodic protection system onto a reinforced concrete structure.
2. Description of the Prior Art
U.S. Pat. No. 2,272,968 discloses a hand-held welding apparatus which has an inner plunger electrode and an outer sleeve electrode. Both electrodes are movable against the force of compression springs. The dimensions of the electrodes are such that the inner plunger electrode makes contact with a workpiece first. After contact is made by the inner electrode, the welding apparatus is then pressed against the workpiece until the outer sleeve electrode makes contact. Further movement of the welding apparatus against the workpiece causes a switch to close connecting the electrodes to a source of current.
The apparatus is useful for spot welding two flat plates together. Both electrodes are applied to one side of one of the plates. The apparatus is not useful for the installation of a mesh anode cathodic protection system to a reinforced concrete structure. It has been found, for such installation, that it is necessary to use a welding tool by which one electrode is applied to one workpiece and the other electrode is applied to the other workpiece. In this way, it is assured that the current flow will be through the interface between the workpieces, providing sufficient heat at the interface to effect the weld joint. In addition, it has been found advantageous, in the installation of a mesh anode cathodic protection system, to have a welding tool which has the capability of application of the electrodes to opposite sides of the workpieces, in some instances, as well as to the same sides of the workpieces, in other instances. The apparatus of U.S. Pat. No. 2,272,968 does not have either of these capabilities. Also, the electrodes in this patent all have special configurations requiring that they be custom machined. The electrodes are not standard resistance welding tool parts.
U.S. Pat. No. 2,644,067 discloses a spot welding apparatus which comprises a pair of electrodes. The electrodes are spaced apart, and supported by a cylindrical body which houses a transformer. Electrical current is supplied to the electrodes through a double-throw switch. The switch is closed by means of an operating handle which is spring mounted on the cylindrical body. The electrodes are not movable with respect to the body against the resistance of a compression spring. Thus, there is no automatic control over the amount of force applied by the electrodes to a workpiece during the welding step. In addition, the electrodes are spaced a substantial distance apart. This means that an excessive amount of power is expended in heating the workpieces, limiting the power available for making a weld. It is disclosed in the patent that for welding together a pair of thin sheets, using the apparatus of the patent, it is necessary to use a backing bar of conducting material to reduce resistance losses during the welding step. The continuous relocation of a backing bar, in the installation of a cathodic protection system onto a concrete structure, would be unduly burdensome.
U.S. Pat. No. 2,471,881 discloses a portable welding device. The device has opposed electrodes for welding two workpieces together from opposite sides of the workpieces. The electrodes are supported by members which can be replaced by other members for different types and sizes of work. The electrodes are not adjustable with respect to the amount of force applied by an electrode against a workpiece during the welding step. The device cannot be employed to weld together two workpieces by application of the electrodes to the same side of the workpieces.